Metal complexes act as catalysts in a redox reaction (redox catalyst) involving electron transfer such as an oxygenation reaction, an oxidative coupling reaction, a dehydrogenation reaction, a hydrogenation reaction, or an oxide decomposition reaction, and are used in production of organic compounds or polymer compounds. Further, the metal complexes are used in various applications including additives, modifiers, cells, sensor materials, and electroluminescence materials.
Among these metal complexes, it is known that the metal complexes including a macrocyclic compound as a ligand form a stable complex due to the effect of the large ring. For example, it is known that porphyrin complexes exhibit stability to acids, compared to non-cyclic complexes (see “Porphyrin no Kagaku” (Chemistry of Porphyrins), published by Kyoritsu Shuppan Co., Ltd. (1982)).
Further, it is known that the metal complexes having a transition metal atom as their center metals exhibit excellent catalyst activity as an oxidative coupling reaction catalyst and hydrogen peroxide decomposition catalyst (see Angewandte Chemie International Edition, 42, 6008 (2003)).
However, the metal complexes including a schiff base as a ligand, as disclosed in Angewandte Chemie International Edition, 42, 6008 (2003), exhibit insufficient stability. Especially when a reaction is conducted in the presence of acids or under heating, the metal complexes exhibit instability to acids or heat, or alternatively both acids and heat for catalyst use. Accordingly, it is strongly desired to improve stability to acids or heat so as to use the metal complexes as a catalyst.